HR: 10:35h
AN: GC32A-02    [Abstracts]
TI: Changes in the timing of snowmelt and associated runoff in the Colorado Rocky Mountains
AU: * Clow, D W
EM: dwclow@usgs.gov
AF: U.S. Geological Survey, MS 415 Federal Center Box 25046, Denver, CO 80225, United States
AB: Previous studies have documented changes in the timing of springtime runoff in the Western United States, with runoff occurring up to two weeks earlier in 1950 than in the 2000. Changes were most pronounced in the Sierra Nevada, Cascades, and northern Rocky Mountains. Few statistically significant changes were identified in Colorado, despite local observations of earlier than normal snowmelt during many recent spring seasons. To further elucidate recent trends in snowmelt timing and associated runoff in Colorado, data from 72 SNOTEL sites and 40 high-elevation streamflow-gaging stations with minimal upstream diversions were tested for trends during 1978 to 2004. Trends were tested using linear regression, as was done in the previous studies, and using the Regional Kendall test (RKT), which is a relatively new test derived from the Seasonal Kendall test. The RKT provides increased power of trend detection in short records with substantial interannual variability. Results indicated that although few sites exhibited statistically-significant trends using linear regression, the RKT identified pervasive earlier snowmelt and runoff throughout the State, with an average change of 0.5 days per year. The RKT revealed important regional variations in the snowmelt- and runoff-timing trends. The strongest trends were in the western and southern parts of Colorado; trends in the north-central part of the State were relatively weak, perhaps because of an increase in upslope storms. Changes in snowmelt timing were strongly correlated with increasing springtime air temperatures, which showed strong positive (warmer) trends during the study period. In contrast with previous studies, this study identified significant shifts in the timing of snowmelt and associated runoff towards earlier in the year in Colorado, and the shift is related to springtime warming.
DE: 0736 Snow (1827, 1863)
DE: 0740 Snowmelt
DE: 1637 Regional climate change
DE: 1807 Climate impacts
DE: 1860 Streamflow
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting